iwlwifi: mvm: Correctly update MAC context on add/del station

Commit "iwlwifi: mvm: don't ask beacons when AP vif and no
assoc sta" directly called iwl_mvm_mac_ctxt_cmd_ap() to update the
MAC context when adding/removing a station. However, this ignores
the case that the vif is actually a P2P GO.

Fix this by calling iwl_mvm_mac_ctxt_changed() that handles P2P GO
case as well.

Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>